"The following instructions :
will void all warranties of your phone!
will erase all your userdata!
will change your current ROM/SPL!
will change your current splash screen!
could brick your phone!
Proceed at your own risk!"
So I've taken the guide that I used to root my myTouch 1.2 with T-Mobile, updated some of the information, and added some explanations. All thanks is owed to The Unlockr for the guide, I'm merely going to attempt to explain what your actually doing in the process and just try make the whole ordeal easier. If I would have known what i was actually doing, it would have taken me 45 minutes to root my phone, vice the good 7-8 hours I put into it. I am by no means an expert on rooting, so feel free to critique what I put in here, and I'll make adjustments as needed.
What's unique about the myTouch 1.2 and the Fender edition is that both phone's have a "perfected" SPL, that does not allow for fastboot access via USB. This means that you can't push any command prompt commands to the phone from your computer, which is what you have to do to get the phone rooted. With these instructions, you'll flash a "non-perfected" SPL onto your phone, load up a custom recovery (which is how you will load up ROM's and do a few other things in the future), and then reflash the phones original "perfected" SPL. Without the original SPL, your phone will not function correctly.
I would suggest opening all the links before continuing so you won't have to wait for the downloads to start as your going. Make sure you remember which link is which tab!!!
From The Unlockr:
I. Setup ABD/Create a Goldcard
Follow this procedure completely to create a working goldcard, then return to this procedure and continue:
How to Create a Goldcard
Follow these instructions without fail. If anything get's messed up here then you won't be able to flash a new SPL and you'll have to attempt to remake the Goldcard again. If you attempt to load the sappimg without using the Goldcard or without a properly done Goldcard, you will get either "Incorrect model ID" or "Main Version is Older". The Goldcard basically tricks the phone into not checking these two parameters, which is what let's you get the "unperfected" SPL on to your phone. ADB is the program that allows you to have a command prompt interface from your computer to your phone.
Note for Windows Vista and Windows 7 users: When your setting up your phones drivers during the ADB setup process, be sure to allow Windows Update to check for drivers. It will allow your computer to automatically install the drivers vice having to manually install them yourself. The option to turn it on should come up when Windows gives the notification that it was unable to install drivers for your device
II. Flash the Sappimg file
1. Download the Sappimg File and save it to your newly created goldcard (NOT in any folders, just on the Goldcard itself).
2. Once the sappimg.zip file is on your goldcard, turn off the phone and put your Goldcard SD into your phone. Then turn it back on by holding down Volume Down and Power. It should boot into bootloader mode and automatically find the sappimg file and ask you to push the trackball to begin the update. Push the trackball and let it update.
*If it tells you Error – Wrong Model ID or anything similar, the goldcard was not created correctly, go back to that procedure and try again.
Here your loading an Engineering SPL, so that we'll be able to get access to the phone via Fastboot USB and load up your new recovery. Be patient once you turn your phone back on, as it will unzip the file, then check the contents. If you get an error, you've got a problem with your Goldcard and need to redo it.
3. Once it finishes flashing press the "Send" button to reboot and you will notice your touchscreen does not work (don’t panic). Turn off the phone, then turn it back on by holding down Back and Power (to get into fastboot mode).
4. Download these two files and save them into C:\AndroidSDK\Tools folder you setup during the ADB setup procedure:
Stock MyTouch SPL
5. Then download the Custom Recovery Image and save it to the C:\AndroidSDK\Tools folder you setup during the ADB setup procedure as well:
Amon Ra’s Recovery
6. Now that you have the recovery, spl and radio all saved in the tools folder of the Android SDK (same folder as the adb program), plug in your phone (while in fastboot mode from step 3).
7. Open the command prompt on your computer and type the following with hitting enter at the end of each line:
A serial number should come up, indicating that your computer can see the phone in fastboot mode. If so continue by typing in the following with hitting enter at the end of each line:
fastboot flash radio radio.img
fastboot flash hboot hboot.nb0 (the 0 at the end of this line is a zero not an oh).
fastboot flash recovery recovery.img
8. Once the phone starts to turn back on begin holding home and power (do not let go until you see the recovery mode) to boot into recovery mode.
This could take a while. I believe the first time I tried to get in I had to hold them down for ~1 minute before getting in. You should see the HTC Magic splash screen pop up first. There is a guide to changing out the splash screen (which is just a picture) within these forums but I'll leave it to you guys to search for it.
9. You should end up in Amon Ra’s recovery mode.
10. At this point, you want to plug your ORIGINAL SD card into your computer and copy the "DCIM" and "Music" folders (if you have them) over to your computer to backup your pictures/video/music. Then take the Goldcard out of your phone and put your ORIGINAL SD back in.
11. With your phone connected via USB to your computer and in Amon Ra's Recovery, highlight USB MS and press the trackball. This should mount your SD card to your computer so that you can move files to it.
12. Download these three .zip files:
614 MHz OC/UV Kernel
You need the OC kernel because there's a known issue with CM 6.1 having a green tint without flashing a new kernel.
13. Copy those three files over to your phone's SD within Windows, "Safely remove hardware" in Windows, then disable USB MS by pressing the Home button. Back out to the main screen.
14. In the recovery select "Wipe" and you want to wipe "data/factory reset" then "Davik-cache".
15. Back out to the main menu and select "Flash zip from sdcard". First you want to select " update-cm-6.1.0-DS-signed.zip" and hit Home to confirm. Once complete, select "Flash zip from sdcard" and this time select "gapps-mdpi-tiny-20101020-signed.zip" and hit Home to confirm. Once complete, one again select "Flash zip from sdcard" and this time select "oc614-cm-22.214.171.124-6.0.0rc2-signed.zip" and hit Home to confirm.
16. Back at the main screen select "Reboot system now". This will load your phone back up as normal and you should now have a working rooted phone with the Cyanogen 6.1 ROM! Jump in there and check it out.
If you want to try out a different ROM, check this thread out. Go to the section called "MT3G 1.2 / LE Fender".
Thanks to Amon Ra for his recovery images!
Thanks to Unlockr for the original How To!
Thanks to the Cyanogen team for an awesome ROM!